IStock Photo 3057414 © Nicholas Campbell

Ninety years ago, the deadliest communicable disease in the US was hands-down the Spanish flu, which killed 1 in 152.9 Americans from 1918 to 1919. While today’s H1N1 flu strain is claiming more than the common flu’s share of victims, it is unlikely that the death tolls for H1N1 and the common flu, even combined, will come anywhere near that of the Spanish flu. However, influenza does find a spot on this list.

At present, the four deadliest communicable diseases in the US are:

1. Human Immunodeficiency Virus (HIV). About 40 million people have HIV worldwide, over 1 million of them in the US. HIV can be transmitted by sexual contact, shared needles, infected blood, or from mother to child. Though several decades of public health campaigns have increased public awareness of the virus, it is still one of the deadliest communicable diseases in America: the odds a person will die of HIV in a year are 1 in 23,630. HIV attacks and disables the body’s white blood cells, leaving it open to any and all secondary infections. This acquired immunodeficiency syndrome (AIDS) is what ultimately kills those infected with HIV, meaning for them even a common cold can be lethal. Most treatments for HIV are anti-retroviral, meant to inhibit the human immunodeficiency virus from replicating itself. However, even with the medications available, HIV has a high mortality rate: the odds a death will be due to HIV are 1 in 195.2. And an unpromising infection rate—the odds a person 13 or older will be diagnosed with HIV in a year are 1 in 4,389—means that for now, HIV is the #1 communicable killer nationwide.

2. Viral Hepatitis. The odds a person will die of viral hepatitis, a disease that attacks the liver, in a year are 1 in 53,610. Hepatitis A, the mildest form of the disease, is contracted either through ingestion of fecal matter (typically from contaminated foods or drinks) or from close contact with someone infected with it. Since it does not cause recurring infection, and only lasts a few weeks or months, the hepatitis A virus (or HAV) is not very dangerous: the odds a person will die of Hepatitis A in a year are 1 in 3,226,000. Hepatitis B and C (HBV and HCV, respectively) are a different story. Like HIV, HBV and HCV are spread by blood-to-blood contact (often from a shared needle or hygiene product) or, in the case of HBV, by sexual contact. Both are chronic liver diseases: once contracted, they are for life, often leading to cirrhosis and liver cancer. HBV/HCV are often present simultaneously, as a “co-infection,” with HIV. There is no vaccine to prevent Hepatitis C, making it particularly pernicious among intravenous drug users and in prison populations. Combined, all forms of viral hepatitis account for 1 in 442.8 deaths in America.

3. Influenza. With the recent heightened awareness of H1N1, or swine flu, it is easy to forget that seasonal flu kills thousands of people each year too. The CDC estimates that each year 200,000 Americans are hospitalized for, and 36,000 die from, the seasonal flu or its complications (e.g. pneumonia or dehydration). The odds a person will die from influenza in a year are 1 in 345,100, or roughly the odds a person will die from choking on food in a year (1 in 343,300). The very young and the very old are most at risk for severe flu complications. For instance, the odds a person 85 or older will die from influenza in a year are 1 in 12,060 (Compare that to the odds a person 25 - 34 will die from influenza in a year: 1 in 6,477,000). Influenza spreads by air (from coughing and sneezing) and on surfaces, and is generally quite contagious: anywhere between 5% and 20% of the US gets the flu each year. Its broad exposure, rather than particular virulence, is what makes influenza deadly.

4. Tuberculosis. Believe it or not, this disease is not just a distant, Keatsian memory. About 22,000 Americans contract tuberculosis in the US each year. While vaccines exist for it, and infection usually relies on prolonged exposure to TB particles in the air, a full-blown case of tuberculosis disease can be quite severe. Symptoms include chronic cough, bloody sputum, weakness, and night sweating. Tuberculosis attacks human lung tissue. The infection itself tends to repeatedly flare and recede, leaving the lungs scarred and coated with cheesy-white dead tissue. The odds a person will die of tuberculosis in a year are 1 in 457,400, though the odds a person will be diagnosed with it in a year are significantly higher: 1 in 21,730. It should be noted that not every case of tuberculosis involves the lungs: tuberculosis can infect any organ (e.g. the brain, the kidneys). The odds are simply higher that someone will die of respiratory tuberculosis in a year (1 in 617,500) than of non-respiratory tuberculosis (1 in 1,764,000). Tuberculosis is also one of the deadliest diseases of all time. In the 20th century alone, it was responsible for around 100 million deaths worldwide, and TB continues to kill about 1 million humans each year.